Content transmission device and content playback device

ABSTRACT

A content transmission unit ( 22 ) is provided that performs chunk transfer of a segment to a client ( 2 ) in subsegment unit, the subsegment being formed by dividing the segment into a plurality of pieces after receiving a request requiring transmission of the segment from the client ( 2 ).

TECHNICAL FIELD

The present invention relates to a content transmission device thattransfers content, a content playback device that acquires content andperforms playback of the content, a content distribution system, amethod for controlling the content transmission device, a method forcontrolling the content playback device, a control program, and arecording medium.

BACKGROUND ART

It has been widespread to distribute large volume content such as amoving image through the Internet with spread of the Internet or highperformance of a computer. For example, there is a service called VideoOn Demand (VOD) which provides content such as a moving image inresponse to a user requirement. For example, as described in PTL 1, inthe VOD, data is transmitted and received between a server (contentproviding device) and a client (content playback device) using HyperTextTransfer Protocol (HTTP).

Here, various techniques have been developed for distribution of thecontent by HTTP. For example, a Motion Picture Experts Group (MPEG) haspromoted an adaptive streaming technique using the HTTP to internationalstandardization as a Dynamic Adaptive Streaming over HTTP (MPEG-DASH)standard.

In the MPEG-DASH, the content is time-divided into a plurality ofsegments and is transmitted in segment unit. Furthermore, each segmentis constituted by one or a plurality of fragments. Furthermore, thecontent is constituted by one or a plurality of periods and one periodincludes one or a plurality of segments.

Furthermore, in the MPEG-DASH, a plurality of Representations areprepared in which quality types (types of bit rate, playback qualitysuch as image, data format, and the like) are different for one content.For example, a plurality of segment data encoded at different bit ratesare prepared for each segment. Thus, the client who receives the contentand performs playback of the content can perform the adaptive streamingby changing the bit rate of the content (segment) to be required inaccordance with a reception status of the content and the like.

Furthermore, in the MPEG-DASH, the content is associated with a MediaPresentation Description (MPD) and the content is managed by the MPD.The MPD is metadata of the content and is obtained by describingmanagement information of the content in an XML format. In other words,the MPD is information that is used in a case where the client acquiresthe content and performs playback of the content.

A detailed description example of the MPD will be described withreference to FIG. 10. FIG. 10 is a diagram illustrating a descriptionexample of the MPD. As illustrated in FIG. 10, information 210 includingtype information 211, profile information 212, buffering timeinformation 213, and distribution start time information 214 isdescribed in a MPD 200.

The type information 211 is information (attribute value of an attribute“type”) indicating whether the distribution is live distribution oron-demand distribution. In the illustrated example, the attribute valueof the attribute “type” is “dynamic” and it indicates that the contentassociated with the MPD 200 is the live distribution content. On theother hand, in a case of the on-demand distribution, “static” isdescribed as the attribute value of the attribute “type”.

The profile information 212 is information indicating a profile of thecontent. Furthermore, the buffering time information 213 is informationindicating a minimum buffering time. In the illustrated example, anattribute value of an attribute “minBufferTime” is “PT10S”, and itindicates that the client performs the buffering of at least 10 seconds.

The distribution start time information 214 is information (attributevalue of an attribute “availabilityStartTime”) indicating a time when aserver starts live streaming distribution of the content. In theillustrated example, the attribute value of the attribute“availabilityStartTime” is “2012-09-20T15:00:00” and it indicates thatthe live streaming distribution is started at 15 o'clock, Sep. 20, 2012.

Furthermore, period information 220 regarding each period that isobtained by dividing a playback duration of the content is described inthe MPD 200. In the illustrated example, as the period information 220,a start time (attribute value of an attribute “start”) of the periodwith the distribution start time of the content as a standard and aduration (attribute value of an attribute “duration”) of the period aredescribed.

Furthermore, acquisition source information 230 indicating anacquisition source of the content is described. In the illustratedexample, as the acquisition source information 230, a URL of the serveris described.

Furthermore, here, as the content, high quality Representation in whicha bit rate is 1024 kbps and low quality Representation in which the bitrate is 512 kbps are prepared. Thus, in the MPD 200, as a segmentcontained in a certain period (from 0 second to 3600 seconds of aplayback time), high quality segment information 241 indicating a highquality segment and low quality segment information 242 indicating a lowquality segment are described. In the high quality segment information241, an ID and a bit rate of the high quality Representation containedin the period are described. Furthermore, a length and a URL of eachsegment contained in the period are described. This also applies to thelow quality segment information 242. Moreover, the period is constitutedby 6 segments of segment #1 to segment #6.

Next, a data structure of basic segment data of the related art will bedescribed with reference to FIG. 11. FIG. 11 is a diagram illustratingthe data structure of the segment data of the high quality segment andthe low quality segment of the related art. Here, an example in whichthe segment data is described in a box format that is defined by ISOBFF(ISO/IEC 14496-12) is described.

As illustrated in FIG. 11(a), a high quality segment 260 of the relatedart is constituted by one Segment Type Box (styp) 261, one Segment IndexBox (sidx) 262, and one or a plurality of sets of Movie Fragment Boxes(moof) 263, 265, 267, and 269, and Media Data Boxes (mdat) 264, 266,268, and 270. Furthermore, as illustrated in FIG. 11(b), similar to thehigh quality segment 260, a low quality segment 280 is constituted byone styp 281, one sidx 282, and one or a plurality of sets of moof 283,285, 287, and 289, and mdat 284, 286, 288, and 290.

The styp 261 and the styp 281 are information indicating the type of thesegment and/or version information and the like. The sidx 262 and thesidx 282 are information regarding a random access point inside thesegment. The moof 263, 265, 267, and 269, the mdat 264, 266, 268, and270, the moof 283, 285, 287, and 289, and the mdat 284, 286, 288, and290 are information regarding a fragment constituting the segment.

One set of the moof and the mdat constitutes one fragment. Furthermore,a unit constituted by one or a plurality of fragments and obtained bydividing the segment to adapt to the random access is referred to as asubsegment. For example, in the example of FIG. 11, the moof 263 and265, and the mdat 264 and 266 constitute one subsegment. A byte size,time information, and the like of each subsegment are described in eachof entries 271, 272, 291, and 292 of the sidx (“s0” and “s1” illustratedin FIGS. 11(a) and 11(b)).

Next, an example of a syntax of the sidx will be described withreference to FIG. 12. FIG. 12 is a diagram illustrating an example ofthe syntax of the sidx. Here, the sidx illustrates an example that isdefined by ISO/IEC 14496-12.

As described above, in the MPEG-DASH, it is assumed to reduce the timelength of the segment for shortening the time until the distribution canbe performed from the generation start of the segment in the server, inorder to support low-delay live streaming. Moreover, since processingdelay by the server and the client, or delay on a network, and the likeoccur, it is not possible for the client to perform playback in realtime in the strict meaning. Thus, the live streaming in substantiallyreal time with slight delay is referred to as a low-delay livestreaming.

CITATION LIST Patent Literature

-   PTL 1: Japanese Unexamined Patent Application Publication No.    2005-110244 (Published on Apr. 21, 2005)

Non Patent Literature

-   NPL 1: “ISO/IEC 23009-1”, [online], Apr. 1, 2012, ISO/IEC, [Searched    on Sep. 26, 2012], Internet <URL:    http://standards.iso.org/ittf/PubliclyAvailableStandards/c05    7623_ISO_IEC_23009-1_2012.zip>

SUMMARY OF INVENTION Technical Problem

As described above, in the MPEG-DASH, the low delay live streaming isrealized by shortening the time length of the segment, but a delay mayoccur due to the shortening of the time length of the segment.Specifically, if the time length of the segment is shortened, typically,in order to cope with network jitter, a plurality of requests requiringtransmission of the segments are transmitted being pipelined. At thistime, if a requested resource is not present in the server and therebyan error occurs, it is necessary to transmit a plurality of requestsagain and there is a problem that the delay occurs by the re-request.

The invention is made in view of the above problem and an object of theinvention is to realize a content transmission device for stablyperforming low-delay live streaming, a content playback device, acontent distribution system, a method for controlling the contenttransmission device, a method for controlling the content playbackdevice, a control program, and a recording medium.

Solution to Problem

In order to solve the above problems, according to an aspect of theinvention, there is provided a content transmission device thattransmits content which is constituted by a plurality of segments and inwhich time information of a plurality of subsegments that are obtainedby dividing the segment is described in a header of the segment to acontent playback device, the content transmission device including:transmission means for transmitting a response to the content playbackdevice in response to a request after receiving the request from thecontent playback device. The transmission means performs chunk transferof the segment to the content playback device in subsegment unit in acase where the request requires transmission of the segment.

Furthermore, in order to solve the above problems, according to anaspect of the invention, there is provided a method for controlling acontent transmission device that transmits content which is constitutedby a plurality of segments and in which time information of a pluralityof subsegments that are obtained by dividing the segment is described ina header of the segment to a content playback device, the methodincluding: a transmission step of transmitting a response to the contentplayback device in response to a request if the request is received fromthe content playback device, in which in the transmission step, thesegment is transferred by chunk transfer to the content playback devicein subsegment unit in a case where the request requires transmission ofthe segment.

Furthermore, in order to solve the above problems, according to anaspect of the invention, there is provided a content playback devicethat acquires content which is constituted by a plurality of segmentsand in which time information of a plurality of subsegments that areobtained by dividing the segment is described in a header of the segmentfrom a content transmission device and performs playback of the content,the content playback device including: acquisition means fortransmitting a request for requiring transmission of the segment to thecontent transmission device. The acquisition means acquires the segmentthat is transferred by chunk transfer from the content transmissiondevice in subsegment unit in response to the request.

Furthermore, in order to solve the above problems, according to anaspect of the invention, there is provided a method for controlling acontent playback device according to an aspect of the invention thatacquires content which is constituted by a plurality of segments and inwhich time information of a plurality of subsegments that are obtainedby dividing the segment is described in a header of the segment from acontent transmission device and performs playback of the content, themethod including: a transmission step of transmitting a requestrequiring transmission of the segment to the content transmissiondevice; and an acquisition step of acquiring the segment that istransferred by chunk transfer from the content transmission device insubsegment unit in response to the request.

Advantageous Effects of Invention

According to the aspects of the invention, it is possible to stablyrealize low-delay live streaming.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a main configuration of a serverand a client according to an embodiment of the invention.

FIG. 2 is a diagram illustrating an outline of a content distributionsystem including the server and the client.

FIG. 3 is a flowchart illustrating an example of a segment transmissionprocess that is performed by the server.

FIG. 4 is a flowchart illustrating an example of a segment acquisitionprocess that is performed by the client.

FIG. 5 is a diagram illustrating a description example of a MPD that isused in the invention.

FIG. 6 is a diagram illustrating an example of an operation sequence ofthe server, the client, and a proxy performing low-delay live streaming.

FIG. 7 is a diagram illustrating an example of HTTP message that istransmitted and received in the low-delay live streaming.

FIG. 8 is a diagram illustrating another description example of the MPDthat is used in the invention.

FIG. 9 is a diagram illustrating a data structure of segment data of ahigh quality segment and a low quality segment which are not the same ina boundary of each subsegment.

FIG. 10 is a diagram illustrating a description example of a MPD of therelated art.

FIG. 11 is a diagram illustrating a data structure of segment data ofthe high quality segment and the low quality segment of the related art.

FIG. 12 is a diagram illustrating an example of a syntax of sidxaccording to the related art.

FIG. 13 is a diagram illustrating an example of an operation sequence ofa server, a client, and a proxy transmitting and receiving a part ofcontent by a byte range request according to the related art.

FIG. 14 is a diagram illustrating an example of a HTTP message that istransmitted and received in live streaming of the related art.

FIG. 15 is a diagram illustrating an example of a configuration of atransfer stream.

FIG. 16 is a block diagram illustrating a main configuration of a serverand a client of another embodiment of the invention.

FIG. 17 is a diagram illustrating a process in which a multiplexedstream is separated on a receiving side.

FIG. 18 is a diagram illustrating an example of a picture and ahierarchy level in the content.

FIG. 19 is a diagram illustrating an example in which isRef and RefPIDis stored in transfer information (program configuration table).

DESCRIPTION OF EMBODIMENTS

The following is description of an embodiment of the invention based onFIGS. 1 to 14. First, an outline of a content distribution system of theembodiment will be described with reference to FIG. 2.

[Outline of Content Distribution System]

FIG. 2 is a diagram illustrating an outline of a content distributionsystem 6 according to the embodiment. As illustrated in FIG. 2, thecontent distribution system 6 includes a server 1, a client 2, a proxy3, a MPD storage device 4, and a segment storage device 5.

As illustrated in FIG. 2, the client 2 is connected to the server 1through the proxy 3. Furthermore, the server 1 is connected to the MPDstorage device 4 and the segment storage device 5. Each device isconnected to an arbitrarily network in a wired or wireless communicationmanner.

The server 1 is a content transmission device that receives a requestfor transmission of the content from the client 2 or the proxy 3 andtransmits the content. The server 1 transmits MPD data to the client 2or the proxy 3 in advance before transmitting data (segment data) of thecontent. Moreover, the server 1 acquires the MPD data and the segmentdata from the MPD storage device 4 and the segment storage device 5 on anetwork 7, but is not limited to this configuration. For example, eachserver 1 may locally hold the MPD data and the segment data.

The client 2 is a content playback device that performs playback of thecontent acquired from other devices such as the server 1 or the contentstored in the client 2. For example, the client 2 is a digitaltelevision, a recorder, a Set Top Box (STB), a PC, a mobile phone, asmart phone, a game machine, a Personal Digital Assistant (PDA), adigital camera, a digital video, and the like.

The proxy 3 is a relay device that transfers data acquired from acertain device (the server 1 or the client 2) to another device (theclient 2 or the server 1). For example, the proxy 3 transfers a requestacquired from the client 2 to the server 1 and transfers the contentacquired from the server 1 to the client 2.

Furthermore, since the proxy 3 caches the data (the MPD and the content)acquired from the server 1, the proxy 3 may be referred to as a CacheServer. Moreover, if the proxy 3 is referred to as the Cache Server, theserver 1 is referred to as an Origin Server. At this time, if the proxy3 acquires the request from the client 2 and holds the content indicatedby the request, the proxy 3 may read and transmit the content to theclient 2.

Furthermore, a configuration of the content distribution system 6 is notlimited to the example illustrated in FIG. 2. For example, the contentdistribution system 6 may include a plurality of servers 1 or mayinclude a plurality of clients 2. Furthermore, the content distributionsystem 6 may include a plurality of proxies 3.

Furthermore, in the embodiment, a transfer protocol on the network inthe content distribution system 6 is HTTP that is widely used as ahypertext transfer protocol. Furthermore, the content that isdistributed by the server 1 is a video content and the content issegmented ISOBFF data. That is, in the embodiment, the contentdistribution system 6 distributes the content based on the MPEG-DASHstandard described above.

Furthermore, the content described in the invention is constituted by aplurality of segments and is content in which time information of theplurality of subsegments that are obtained by dividing the segment isdescribed in a header of the segment. The time information of thesubsegment is information indicating a time position of the subsegmentand, for example, is information indicating a playback start time of thesubsegment. Furthermore, in the invention, the segment may be dividedinto the subsegments in any unit, and, for example, the segment may bedivided into the subsegments so that random access can be performed insubsegment unit. In other words, information indicating the timeposition of a random access point as time information of the subsegmentmay be described in a header of the segment.

[Configuration of Each Device]

Next, a main configuration of the server 1 and the client 2 will bedescribed with reference to FIG. 1. FIG. 1 is a diagram illustrating anexample of the main configuration of the server 1 and the client 2.Moreover, in FIG. 1, the proxy 3 is omitted.

(Server)

As illustrated in FIG. 1, the server 1 is constituted by a servercontrol unit 11, a server storage unit 12, and a server communicationunit 13.

The server communication unit 13 performs communication with otherdevices such as the client 2, the proxy 3, the MPD storage device 4, andthe segment storage device 5 by wireless communication means or wiredcommunication means, and performs exchange of the data according to aninstruction of the server control unit 11.

The server control unit 11 performs various calculations by executingprograms that is read with a temporal storage unit (not illustrated)from the server storage unit 12 and collectively controls the unitsincluded in the server 1.

In the embodiment, the server control unit 11 includes a contentacquisition unit 21 and a content transmission unit (transmission means)22 as functional blocks. Each functional blocks (21 and 22) of theserver control unit 11 can be realized when a central processing unit(CPU) reads and executes a program stored in a storage device realizedby a read only memory (ROM) and the like with the temporal storage unitrealized by a random access memory (RAM) and the like.

The content acquisition unit 21 acquires the MPD data from the MPDstorage device 4 or the segment data from the segment storage device 5based on an instruction from the content transmission unit 22. Thecontent acquisition unit 21 outputs the acquired MPD data or the segmentdata to the content transmission unit 22.

Moreover, the content acquisition unit 21 may acquire the MPD dataand/or the segment data in advance regardless of presence or absence ofthe instruction from the content transmission unit 22. In this case, thecontent acquisition unit 21 stores the MPD data and the segment datathat are acquired in the server storage unit 12 in advance and reads theMPD data and the segment data from the server storage unit 12 based onthe instruction from the content transmission unit 22.

The content transmission unit 22 determines whether or not the receivedrequest is a request requiring the transmission of the segment in a caseof receiving the request from the client 2. If the received request isthe request requiring the transmission of the segment, the contenttransmission unit 22 instructs the content acquisition unit 21 toacquire the segment, acquires the segment data from the contentacquisition unit 21, and transmits a response including the segment datato the client 2.

However, in the invention, the content transmission unit 22 does nottransmit all the segment data at a time, but transmits the segment datain chunk unit in a case of transmitting the segment data. A plurality ofsubsegments formed by dividing the segment constitutes one chunk.

On the other hand, if the received request is not the request forrequiring the transmission of the segment, the response to the requestis transmitted to the client 2. For example, if the request forrequiring the transmission of the content management information (MPD)is received from the client 2, the content transmission unit 22instructs the content acquisition unit 21 to acquire the MPD of thecontent and if the MPD data is acquired from the content acquisitionunit 21, the content transmission unit 22 transmits the responseincluding the acquired MPD data to the client 2. Furthermore, whenreceiving a request for requiring transmission of a resource such as aWeb page from the client 2, the content transmission unit 22 instructsthe content acquisition unit 21 to acquire the resource and if theresource is acquired from the content acquisition unit 21, the contenttransmission unit 22 transmits the response including the acquiredresource to the client 2.

Moreover, the content transmission unit 22 may determine whether or notthe received request is the request for requiring the transmission ofthe segment based on whether or not a media type of the resourcedesignated by the received request is the segment.

The server storage unit 12 stores a program or data, and the likereferred to by the server control unit 11 and, for example, may storethe MPD data and the segment data acquired by the content acquisitionunit 21.

(Client)

As illustrated in FIG. 1, the client 2 includes a client control unit41, a client storage unit 42, a client communication unit 43, a displayunit 44, and an audio output unit 45. Moreover, the client 2 may includean operation unit, an audio input unit, and the like, but the units arenot illustrated because the units have no relationship with thecharacteristics of the invention.

The client communication unit 43 performs communication with otherdevices such as the server 1 and the proxy 3 by wireless communicationmeans or wired communication means and performs exchange of dataaccording to instruction of the client control unit 41.

The display unit 44 displays an image according to instruction of theclient control unit 41. The display unit 44 may display the imageaccording to the instruction of the client control unit 41 and, forexample, a liquid crystal display (LCD), an organic EL display, a plasmadisplay, and the like may be used as the display unit 44.

The audio output unit 45 receives an electrical signal from the clientcontrol unit 41, converts the received electrical signal to sound, andoutputs the sound to the outside of the client 2. The audio output unit45 is a so-called speaker.

The client control unit 41 performs various calculations andcollectively controls the units included in the client 2 by executingthe programs read by the temporal storage unit (not illustrated) fromthe client storage unit 42.

In the embodiment, the client control unit 41 includes a contentacquisition unit (acquisition means) 51 and a content playback unit 52as a functional block. Each of the functional blocks (51 and 52) of theclient control unit 41 can be realized by reading and executing thetemporal storage unit in which a CPU realizes a program, using a RAM andthe like, stored in a storage device realized by a ROM and the like.

The content acquisition unit 51 transmits the request to the server 1through the client communication unit 43 and acquires the content (theMPD associated with the content and the segment configuring the content)from the server 1.

Specifically, the content acquisition unit 51 transmits the requestrequiring the transmission of the management information (MPD) of thecontent to the server 1 or the proxy 3 if content acquisition (playback)instruction is input from a user through an operation unit (notillustrated). Then, the content acquisition unit 51 receives the MPDdata of the content as the response of the request. The contentacquisition unit 51 transmits the request requiring the transmission ofthe segment configuring the content to the server 1 or the proxy 3referring to the received MPD data. Then, the content acquisition unit51 acquires the segment data of the content as the response of therequest. The content acquisition unit 51 outputs the acquired segmentdata to the content playback unit 52.

Furthermore, if delay and the like of the network occur, the contentacquisition unit 51 executes acquired Representation switching. At thistime, then, if a part of remaining segment is acquired, the contentacquisition unit 51 specifies a byte range of the subsegment includingnon-acquired data and transmits the request with a byte range templateto the server 1 or the proxy 3 based on the specified byte range.

The content playback unit 52 refers to the MPD data and performsplayback of the content based on the acquired segment data in a case ofacquiring the segment data from the content acquisition unit 51.

The client storage unit 42 stores a program or data, and the likereferenced by the client control unit 41 and, for example, may store theMPD data and the segment data acquired by the content acquisition unit51.

[Process of Server]

Next, a segment transmission process of the server 1 will be describedwith reference to FIG. 3. FIG. 3 is a flowchart illustrating an exampleof the segment transmission process of the server 1.

As illustrated in FIG. 3, the server 1 receives a HTTP request messagerequiring transmission of the segment or a part of the segment from theclient 2 (S61). The content transmission unit 22 instructs the contentacquisition unit 21 to acquire the segment and acquires the segment datafrom the content acquisition unit 21. Then, the content transmissionunit 22 transmits, to the client 2, the segment by chunk unit in whichthe plurality of subsegments formed by dividing the segment are used asone chunk (S62).

The content transmission unit 22 transmits the segment by chunk unit andif an entire required segment is transmitted (YES in S63), the segmenttransmission process is completed. Otherwise, if connection is closed inthe middle thereof (YES in S63), the segment transmission process iscompleted by the content transmission unit 22.

[Process of Client]

Next, a segment acquisition process of the client 2 will be describedwith reference to FIG. 4. FIG. 4 is a flowchart illustrating an exampleof the segment acquisition process of the client 2.

As illustrated in FIG. 4, first, the content acquisition unit 51 refersthe MPD data and transmits the request requiring the transmission of asegment (for example, a high quality segment) of initial Representation(S71).

After the request is transmitted, the content acquisition unit 51determines whether or not Representation is switched (S72). Here, if thedelay and the like of the network does not occur, the contentacquisition unit 51 acquires the segment that is chunk-transferred bysubsegment unit from the server 1 (S73) without Representation switching(NO in S72). The content acquisition unit 51 determines whether or notthe entire requested segment is received (S74), and if the entirety isnot received (NO in S74), the process proceeds returns to S72.

Here, if the delay and the like of the network occur, the contentacquisition unit 51 switches Representation of the acquired segment (YESin S72). The content acquisition unit 51 analyzes sidx of Representation(for example, low quality segment) of a switching source and specifies abyte range of a non-acquired subsegment based on an access point of thenon-acquired subsegment of the requested segments (S75). The contentacquisition unit 51 generates a byte range template URL indicating anacquisition source of the non-acquired subsegment based on the specifiedbyte range (S76). The content acquisition unit 51 transmits the requestfor requiring the transmission of the remaining data (data from themiddle thereof) of the segment based on the generated URL (S77). Then,the content acquisition unit 51 acquires the segment of epresentation ofthe switching destination by chunk unit from the middle thereof (S73).

Thus, the process until the entire segment is received is performed andif the entire segment is received (YES in S74), the segment acquisitionprocess is completed.

[Description Example of MPD]

Next, a description example of the MPD used in the invention will bedescribed with reference to FIG. 5. FIG. 5 is a diagram illustrating thedescription example of the MPD used in the invention.

As illustrated in FIG. 5, profile information 112 and acquisition sourceinformation 130, that are included in information 110, of a MPD 100 usedin the invention are different from those of the MPD 200 of the relatedart illustrated in FIG. 10.

Specifically, in the MPD 100,“urn:mpeg:dash:profile:isoff-low-latency-live:2012” indicating low delaylive distribution is described in the profile information 112.Furthermore, the byte range template (BaseURL@byterange) is described inthe acquisition source information 130 instead of the URL of a mereserver.

[Byte Range Request]

In the related art, if the client 2 acquires a part of the content, theclient 2 can acquire a part thereof by a byte range request defined inHTTP/1.1. However, in the response from the server 1 with respect to thebyte range request, since a status code is “206”, the proxy 3 does notcache the data included in the response. Thus, even if the same contentis re-requested to the server 1 through the proxy 3, since the proxy 3is not cached, the server 1 must transmit the content. Thus, it isdifficult to stably realize low delay live streaming.

An operation sequence of the server, the client and the proxy thattransmit and receive a part of the content by the byte range request,and a HTTP message that is transmitted and received in live streaming ofthe related art will be described with reference to FIGS. 13 and 14 indetail below. FIG. 13 is a diagram illustrating an example of theoperation sequence of the server, the client, and the proxy thattransmit and receive a part of the content by the byte range request.Furthermore, FIG. 14 is a diagram illustrating an example of the HTTPmessage that is transmitted and received in live streaming of therelated art.

As illustrated in FIGS. 13 and 14, first, the client refers the MPD 200and transmits a request message 301 for requiring transmission of amessage #1 to the proxy. The proxy receives the request message 301 andsince a segment #1 is not cached, the proxy transfers the request as itis and transmits a request message 302 to the server.

Since the request message 302 requires the transmission of the segment,the server transmits a response message 303 including a data body of thesegment #1 to the proxy as the response of the request message 302. Theproxy receives the response message 303 and since a status code of theresponse message 303 is “200”, the proxy performs caching 304 of thedata included the response message 303, transfers the response as it is,and transmits a response message 305 to the client. The client receivesthe response message 305 and acquires the segment #1.

Here, since the delay of the network and the like occur, the clientexecutes representation switching 306. Then, the client analyzes thesidx and specifies byte ranges (xxx to yyy) of the non-acquired data ofthe segment #1. The client transmits a byte range request message 307 tothe proxy based on the specified byte range. The proxy receives therequest message 307 and also in here, since the data indicating therequest is not cached, the proxy transfers the request as it is andtransmits a request message 308 to the server.

Since the request message 308 is the byte range request, the server 1transmits a response message 309 of a status code “206” including thedata of a designated byte range that is a part of the segment #1 to theproxy as the response of the request message 308. The proxy receives theresponse message 309 and since the status code of the response message309 is “206”, the proxy does not cache the data included in the responsemessage 309 and transfers the response as it is, and transmits aresponse message 310 to the client. The client receives the responsemessage 310 and acquires the remaining data of the segment #1.

As described above, if a part of the content is transmitted and receivedby the byte range request, since the status code of the response is“206”, the proxy 3 does not cache. Moreover, the data that is cached bythe proxy 3 is the data included in the response in which the statuscode is “200”, “203”, “300”, “301”, or “410”.

In the MPEG-DASH, it is also possible to realize low delay livestreaming by reduction of a Round Trip Time (RTT) by cache hit in theproxy 3 that is a cache server. Thus, if there is data that is notcached by the proxy 3, it is difficult to stably realize the low delaylive streaming.

In a case of acquiring a part of the segment in the byte range request,in order to solve the above problem that is not cached in the proxy 3,in the invention, a part of the segment is acquired in the request usingthe byte range template described above. As described below, in responseto the request using the byte range template, since the status code is“200”, the proxy 3 can cache the data included in the response.

First Embodiment

Next, the operation sequence of the server 1, the client 2, and theproxy 3 executing the low delay live streaming, and the HTTP messagethat is transmitted and received in the low delay live streaming will bedescribed with reference to FIGS. 6 and 7. FIG. 6 is a diagramillustrating an example of the operation sequence of the server 1, theclient 2, and the proxy 3 executing the low delay live streaming.Furthermore, FIG. 7 is a diagram illustrating an example of the HTTPmessage that is transmitted and received in the low delay livestreaming.

As illustrated in FIGS. 6 and 7, first, the client 2 refers a MPD 70 andtransmits a request message 81 for requiring the transmission of themessage #1 to the proxy 3. The proxy 3 receives the request message 81and, since the message #1 is not cached, the proxy 3 transfers therequest as it is, and transmits a request message 82 to the server 1.

Since the request message 82 requires the transmission of the segment,the server 1 transmits a response message 83 including the data body ofthe segment #1 that is chunk-divided by subsegment unit to the proxy 3as the response of the request message 82. The proxy 3 receives theresponse message 83 and since the status code of the response message 83is “200”, the proxy 3 performs caching 84 of data included in theresponse message 83, transfers the response as it is, and transmits aresponse message 85 to the client 2. The client 2 receives the responsemessage 85 and acquires the segment #1 that is chunk-transferred bysubsegment unit.

Here, since the delay and the like of the network occur, the client 2executes Representation switching 86. The client 2 analyzes the sidx andspecifies the byte ranges (xxx to yyy) of the subsegment including thenon-acquired data of the segment #1. The client 2 transmits a requestmessage 87 using the byte range template to the proxy 3 based on thespecified byte range rather than the byte range request. The proxy 3receives the request message 87 and since the data indicating therequest is also not cached, the proxy 3 transfers the request as it isand transmits a request message 88 to the server 1.

Since the request message 88 is a usual request rather than the byterange request, the server 1 transmits a response message 89 of thestatus code “200” including the subsegment of the designated byte rangeas the response of the request message 88 to the proxy 3 by chunk unit.The proxy 3 receives the response message 89 and since the status codeof the response message 89 is “200”, the proxy 3 performs caching 90 ofthe data included in the response message 89, transfers the response asit is, and transmits a response message 91 to the client 2. The client 2receives the response message 91 and acquires the remaining data of thesegment #1 by chunk unit.

[Other Description Example of MPD]

In the invention, the segment is further divided into the plurality ofsubsegments, but a time length of the subsegment may be arbitrarily.That is, the time length of each subsegment may not be constant and thetime lengths of the subsegments may be different from each other.

Furthermore, in the invention, since the chunk transfer is performed bysubsegment unit, the time length of the subsegment matches a time lengthof one chunk. The client 2 can predict a delay amount in the livestreaming by grasping the time length of the chunk in advance. Thus, itis preferable that the time length of the chunk is described in the MPD.If the time length of the chunk is fixed, for example, the time lengthof the chunk may be described in the MPD. Furthermore, if the timelength of the chunk is variable, for example, the maximum value and/orthe minimum value of the time length of the chunk may be described inthe MPD. A description example of the time length of the chunk will bedescribed below.

Furthermore, in the MPEG-DASH, in order to switch Representation, it ispreferable that boundaries of the subsegments respectively correspondingbetween Representations are uniform. In other words, it is preferablethat playback start times of the subsegments respectively correspondingbetween Representations match each other. In this case, even ifRepresentation is switched, since the playback times of the subsegmentsare match each other, it is possible to perform the playbackparticularly without a problem.

On the other hand, if the boundaries of the subsegments correspondingbetween Representations are not uniform, since the boundaries must bemade uniform and the playback is performed after switching ofRepresentation, it is preferable the client 2 grasps whether or not theboundaries of the subsegments are uniform in advance. Thus, it ispreferable that information regarding arrangement of the subsegmentsindicating whether or not the boundaries of the subsegments are uniformis described in the MPD. The information regarding the arrangement ofthe subsegments will be described later.

Next, another description example of the MPD using in the invention willbe described with reference to FIG. 8. FIG. 8 is a diagram illustratinganother description example of the MPD using in the invention. In FIG.8, an example of the MPD in which the information regarding thearrangement of the subsegments and the information regarding the timelength of the chunk are described is illustrated.

As illustrated in FIG. 8, in MPD 101 used in the invention, theinformation regarding the arrangement of the subsegments and theinformation regarding the time length of the chunk are additionallydescribed as comparing with the MPD 100 illustrated in FIG. 5.

Specifically, an attribute “AdaptationSet@subsegmentAlignment” and anattribute value “true” thereof are described in the MPD 101 asinformation 150 regarding the arrangement of the subsegments. Theattribute value “true” indicates that the boundaries of the subsegmentsare uniform and if the boundaries of the subsegments are not uniform,“false” is described as the attribute value.

Furthermore, in the MPD 101, an attribute “maxChunkDuration” and anattribute value “PT10S” are described in high quality segmentinformation 143 and low quality segment information 144 as theinformation regarding the time length of the chunk. The attribute“maxChunkDuration” indicates the maximum value of a variable time lengthof the chunk and the attribute value “PT10S” indicates that the maximumvalue is 10 seconds. As described above, as the information regardingthe time length of the chunk, the attribute “chunkDuration” indicatingthe fixed time length of the chunk may be described or an attribute“minChunkDuration” indicating the minimum value of the variable timelength of the chunk may be described.

Furthermore, the attribute “chunkDuration” described above may beinterpreted as a time length of an initial chunk of the segment.Otherwise, an attribute “chunkDurationOffset” indicating a differencevalue between the time length (equal to a value of an attribute“SegmentList@duration”) of the segment and the time length (equal to avalue of an attribute “SegmentList@chunkDuration”) of the initial chunkof the segment may be described instead of the attribute“chunkDuration”.

[Exchanging Example of Representation if Boundaries of Subsegments arenot Uniform]

Next, if the boundaries of the subsegments are not uniform, switching ofRepresentations will be described with reference to FIG. 9. FIG. 9 is adiagram illustrating a data structure of the segment data of the highquality segment and the low quality segment which are not the same inthe boundaries of the subsegments.

As illustrated in FIG. 9(a), a high quality segment 160 of 1024 kbpsincludes a subsegment #0 formed of a moof 163 and a mdat 164, thesegment #1 formed of a moof 165 and a mdat 166, and a segment #2 formedof moof 167 and 169, and mdat 168 and 180. On the other hand, a lowquality segment 180 of 512 kbps includes a subsegment #0 formed of amoof 183 and a mdat 184, the segment #1 formed of moof 185 and 187, andmdat 186 and 188, and a segment #2 formed of a moof 189 and a mdat 190.That is, the playback start time of the segment #2 is different in thehigh quality segment 160 and the low quality segment 180.

Moreover, a time length of a fragment (moof and mdat) included in thehigh quality segment 160 and the low quality segment 180 is constant.That is, fragments 163 to 170 of the high quality segment respectivelycorrespond to fragments 183 to 190 of the low quality segment.

Here, Representation is switched and the low quality segment is acquiredafter acquiring to the segment #1 of the high quality segment. In thiscase, the data to be acquired next is the moof 187 of the low qualitysegment corresponding to the moof 167 of the high quality segment.However, in the low quality segment 180, since the moof 185 and 187, andthe mdat 186 and 188 become the subsegment #1, it is not possible toacquire only after the moof 187. Thus, the acquisition is started fromthe subsegment #1 including the moof 187 that is the non-acquired datasuch that a gap does not occur in a case of performing the playback. Atthis time, the moof 185 and the mdat 186 are obtained by beingoverlapped in time, but the live streaming is realized by adjusting themoof 185 and the mdat 186 in a case of performing the playback.

Moreover, as described above, time information of each subsegment isdescribed in the sidx 162 and 182 that is a header of the segment andthe byte range is specified by analyzing the sidx.

CONCLUSION

According to an aspect of the invention, there is provided a contenttransmission device that transmits content which is constituted by aplurality of segments and in which time information of a plurality ofsubsegments that are obtained by dividing the segment is described in aheader of the segment to a content playback device, the contenttransmission device including transmission means for transmitting aresponse to the content playback device in response to a request afterreceiving the request from the content playback device. The transmissionmeans performs chunk transfer of the segment to the content playbackdevice in subsegment unit in a case where the request requirestransmission of the segment.

According to an aspect of the invention, there is provided a method forcontrolling a content transmission device that transmits content whichis constituted by a plurality of segments and in which time informationof a plurality of subsegments that are obtained by dividing the segmentis described in a header of the segment to a content playback device,the method including a transmission step of transmitting a response tothe content playback device in response to a request if the request isreceived from the content playback device. In the transmission step, thesegment is transferred by chunk transfer to the content playback devicein subsegment unit in a case where the request requires transmission ofthe segment.

In the above configuration, the transmission means perform chunktransfer of the segment by dividing the segment into a plurality ofsubsegments in response to the request requiring the transmission of thesegment. That is, the segment is transmitted in subsegment unit that isshorter in time than in segment unit and the transfer of the pluralityof subsegments can be required by one request. Thus, it is possible tosuppress an error process associated with pipelining of a plurality ofrequests while shortening a time until the distribution can be performedfrom the generation start of the subsegment. Accordingly, it is possibleto stably realize the low delay live streaming.

Furthermore, in the content transmission device according to an aspectof the invention, the segment may be divided into the subsegments so asto enable random access in subsegment unit.

Furthermore, in the content transmission device according to an aspectof the invention, the transmission means may transmit content managementinformation in which the time length of the subsegment is described tothe content playback device in a case where the time length of eachsubsegment is constant.

Furthermore, in the content transmission device according to an aspectof the invention, the transmission means may transmit content managementinformation in which at least one of the maximum value and the minimumvalue of the time length of the subsegment is described to the contentplayback device in a case where the time length of each subsegment isdifferent.

In the above configuration, since the client can grasp the time lengthof the subsegment that is chunk-transferred, it is possible to predictthe delay amount in the live streaming.

According to an aspect of the invention, there is provided a contentplayback device that acquires content which is constituted by aplurality of segments and in which time information of a plurality ofsubsegments that are obtained by dividing the segment is described in aheader of the segment from a content transmission device and performsplayback of the content, the content playback device includingacquisition means for transmitting a request for requiring transmissionof the segment to the content transmission device. The acquisition meansacquires the segment that is transferred by chunk transfer from thecontent transmission device in subsegment unit in response to therequest.

According to an aspect of the invention, there is provided a method forcontrolling a content playback device that acquires content which isconstituted by a plurality of segments and in which time information ofa plurality of subsegments that are obtained by dividing the segment isdescribed in a header of the segment from a content transmission deviceand performs playback of the content, the method including atransmission step of transmitting a request requiring transmission ofthe segment to the content transmission device; and an acquisition stepof acquiring the segment that is transferred by chunk transfer from thecontent transmission device in subsegment unit in response to therequest.

Second Embodiment

Regarding the delay occurring on the network between the server and theclient, in the first embodiment, if an error occurs due to the fact thatthe resource requested by the client does not exist in the server, thereis a problem that a load is applied on the network and the client, andthe delay occurs because a plurality of requests are transmitted again.Regarding the delay occurring in the client, since a processing abilityof a decoder included in the client is low, there is also a problem thata load is applied and the delay occurs in the decode process.

In the embodiment, a method for eliminating the delay occurring during adecoding process by extracting appropriate information in the contentdepending on a decode processing ability of the client will be describedbelow with reference to FIGS. 15 to 18. FIG. 15 is a diagramillustrating an example of a configuration of a transfer streamaccording to the embodiment. FIG. 16 is a block diagram illustrating amain configuration of the server and the client of the embodiment.Furthermore, FIG. 17 is a diagram illustrating a process in which astream obtained by multiplexing a plurality of frame rate data accordingto the embodiment is separated on a receiving side. FIG. 18 is a diagramillustrating a picture and a hierarchy level in the content according tothe embodiment.

In current digital broadcasting, a broadcasting station corresponding tothe server stores a plurality of data of video, audio, and other programinformation respectively in a plurality of packets, and transmits thepackets by multiplexing the packets into one stream. For themultiplexing, a MPEG-2 TS (transport stream) is used which is a streamformat of MPEG. Multiplexed transport stream (TS) is separated into eachpacket by a broadcasting receiver that is the client and data such asvideo or audio, and the like are acquired.

FIG. 15(a) illustrates a structure of the TS of the related art. The TSis constituted by an assembly of TS packets respectively having 188bytes. The TS packets are input into the client in time series manner.At this time, as illustrated in FIG. 15(a), a Packet Identifier (PID)indicating type of data in the packet is allocated to a header of eachTS packet and a separating unit identifies and separates video, audio,associated information, and the like stored in a payload of the packetusing this value, and then can input the data to an appropriate decoder.

In the TS, the same PID is allocated to the packets in which the videodata composed of a plurality of video qualities that are scalable codedis separated and stored. Then, the client can separate the plurality ofvideo qualities in a stage of a decoding process. That is, one videodata is transmitted with one PID.

On the other hand, in the TS of the related art, the contents to whichdifferent PID are allocated cannot be recognized as the same content.For example, in the video data compressed by a predictive codingcompression standard such as a HEVC, frames can be respectivelycompressed as different pictures in which prediction methods aredifferent from each other such as I, P, and B, and can be respectivelytransmitted by being stored in different packets. However, it is notpossible to identify whether the picture data stored in the packet is I,P, or B at the TS level. At this time, if there is the B picture that isnot referred to for decoding of other pictures, even if the data of theB picture is removed, the playback can be performed. Thus, it ispossible to appropriately remove the packet of the B picture datadepending on ability of the client and to perform the playback bychanging a frame rate for each client by utilizing this property.However, in a case of transmitting the packet using the TS, as describedabove, since the packet cannot be identified by the multiplexingseparation unit, such a process cannot be performed.

As illustrated in FIG. 15(b), in the embodiment, the packets to whichdifferent PID are allocated can be recognized as the same content byallocating a RefPID (dependency identifier) indicating that those arethe same content in addition to the PID in order to solve the aboveproblem. Furthermore, in the embodiment, the packet includes a flagisRef indicating whether or not the packet includes a RefPID. The isRefis a binary flag, indicates that the RefPID is included in a case of 1,and indicates that the RefPID is not included in a case of 0.

FIG. 16 is a block diagram illustrating a main configuration of theembodiment. As illustrated in FIG. 16, the server includes amultiplexing unit that multiplexes the plurality of packets and theclient includes the multiplexing separation unit that separates thestream in which the plurality of packets received from the server aremultiplexed into individual packets. Moreover, in the server and theclient illustrated in FIGS. 1 and 16, description regarding the samemembers will be appropriately omitted.

(Server)

A server transmission unit transmits the data to the client by wirelesscommunication means or wired communication means.

A server control unit includes a content generation unit, a multiplexingunit, and a content transmission unit (transmission means) as functionalblocks. Here, the content generation unit generates content data andoutputs the content data to the content transmission unit by performingseparation and multiplexing the content data to the packet in themultiplexing unit. For example, a value pid_b of the PID is allocated tothe packet in which the P picture data is stored and a value pid_a ofthe PID is allocated to the packet in which the B picture data isstored. Furthermore, in the packet in which the B picture data isstored, the value of isRef is 1 and the RefPID of the value pid_b isallocated to the packet.

(Client)

A client receiving unit receives data from the server by wirelesscommunication means or wired communication means.

A client control unit includes a content acquisition unit (acquisitionmeans), a multiplexing separation unit, and a content playback unit asfunctional blocks. Here, the content acquisition unit acquires amultiplexing stream transmitted from the server and outputs themultiplexing stream to the multiplexing separation unit.

The multiplexing separation unit separates the multiplexing stream intorespective packets. At this time, the multiplexing stream is separatedto the packets such as video, audio, and program information byreferring to the value of the PID.

Furthermore, the multiplexing separation unit determines whether thepacket includes the RefPID and if the packet includes the RefPID, thedata of the packet and the data of the packet that is indicated by theRefPID are interpreted as the data of one content. Then, the data ofeach content that is separated by the multiplexing separation unit isinput into the content playback unit.

Moreover, at this time, in the data of the packet and the data of thepacket that is indicated by the RefPID, transmission time information(not illustrated) is stored in each packet header and it is possible todetermine the order uniquely by seeing the transmission timeinformation. Otherwise, the order may be determined uniquely from thesequence number by storing the sequence number (not illustrated) in thepacket header.

The content playback unit sequentially decodes the packet data of thevideo separated by the multiplexing separation unit according to the PIDand RefPID into a video signal, appropriately rearranges decoded picturedata to a display order, and then outputs the picture data in thedisplay unit, respectively.

As described above, FIG. 17 is a diagram illustrating that the stream inwhich the I and P picture data and the B picture data are respectivelystored and multiplexed in the packet of the value pid_b of the PID andthe packet of the value pid_a of the PID is received, and the receivedmultiplexed stream is multiplexed and separated to the content data inwhich the frame rate is different based on the PID and RefPID in themultiplexing separation unit of the client. At this time, the I and Ppicture data are encoded data of a frame rate of 60 Hz. On the otherhand, the B picture data is additional data for performing the playbackof 120 Hz by sandwiching one sheet of the B picture between pictures ofthe I and P picture data. Specifically, since the RefPID of pid_a ispid_b, and the playback of the video of 120 Hz is performed byoutputting entire packets of the pid_a and the pid_b to a video decoder.On the other hand, if only the pid_b is output to the video decoder, theplayback of video of 60 Hz is performed.

Moreover, in the embodiment, a configuration is provided in which theisRef and the RefPID are allocated to the packet header, but the storingposition is not limited to the embodiment, and for example, the isRefand the RefPID may be described in the MPD that is stored in the MPDstorage device illustrated in FIG. 16 similar to the description in thefirst embodiment. Otherwise, the isRef and the RefPID may be describedas a part of metadata of transfer information regarding the transfer ofthe content or the playback information relating to the playback of thecontent instead of the MPD. Otherwise, furthermore, informationindicating that the contents are the same content as each other may bedescribed in a value of the PID and the RefPID is not allocated by usingthe PID also as the RefPID. Furthermore, a configuration may be adoptedin which the RefPID is essential and the isRef is omitted.

An example is illustrated in FIG. 19(a) in which the isRef and theRefPID are stored in the transfer information based on a ProgramAssociation Table/Program Map Table (PAT/PMT) used in current digitalbroadcasting. Furthermore, an example is illustrated in FIG. 19(b) inwhich a plurality of PID are described instead of using the isRef andthe RefPID. In a case of FIG. 19(b), the video is illustrated to beformed of data to which two PID are allocated and the PID that iswritten later is interpreted to depend on the PID that is writtenearlier. The multiplexing separation unit knows the PID of necessarydata, separates only the packet data to which the PID is allocated fromthe multiplexing stream, and performs the playback thereof by using thetransfer information.

Thus, the client can identify the packet including the same contentholding different PID in the multiplexing stream and can decode thepacket by acquiring required packet data according to decodingcapability. In the above example, an example is illustrated in which theplayback having different frame rates of 60 Hz and 120 Hz is performedfrom the packet storing the I and P picture data, and the B picturedata. In addition, for example, in scalable coding, stream data of a lowresolution base layer and stream data of a high resolution enhancementlayer are stored in the packets having different PID and are identifiedusing the PID and the RefPID. Thus, it is possible to perform a processin which the client having low decoding capability acquires data of thebase layer and performs the playback of the low resolution video, andthe client having high decoding capability acquires data of base andenhancement layer, and performs the playback of the high resolutionvideo. It is possible to eliminate the delay occurring in the decodingby extracting the data having an appropriate frame rate and appropriateresolution depending on the decoding capability.

Furthermore, allocation of the PID and RefPID to the I, P, and Bpictures is not limited to the above example, and as illustrated in FIG.18, if the B picture consisting of a plurality of hierarchies isprovided, the PID having a value pid_0 is allocated to the packet(hierarchy 0) of the I/P picture and the PID having a value of pid_1 isallocated to the packet of the B picture of the hierarchy 1. Similarly,the PID having values pid_2 and pid_3 may be allocated to the packet ofthe B picture of hierarchies 2 and 3. In this case, the RefPID havingthe value of pid_0 is allocated to the packet of the B picture of thehierarchy 1 and similarly, the RefPID having values of pid_1 and pid_2is allocated to the packet of the B picture of the hierarchies 2 and 3.

In the above configuration, the acquisition means acquire the segmentthat is chunk-transferred in subsegment unit that is obtained bydividing the segment into a plurality of pieces in response to therequest requiring the transmission of the segment. That is, the segmentmay be transmitted in subsegment unit that is shorter in time than insegment unit and it is possible to request the transmission of theplurality of subsegments in one request. Thus, it is possible tosuppress an error process associated with pipelining of a plurality ofrequests while shortening the time until the distribution can beperformed from the generation start of the subsegment.

Furthermore, in the content playback device according to an aspect ofthe invention, the segment may be divided into the subsegments so as toenable random access in subsegment unit.

Furthermore, in the content playback device according to an aspect ofthe invention, the acquisition means may specify a byte range of thesubsegment including a part of the segment and transmit the requestusing a byte range template that designates the specified byte range ina case where the acquisition means transmits a request for requiringtransmission of a part of the segment.

In the above configuration, if the acquisition means transmits therequest requiring the transmission of a part of the segment, since theacquisition means transmits the request using the byte range template,the status code of the response to the request is “200”. Thus, if thecontent is acquired through the proxy that is a relay device of thecontent, the proxy can cache the data included in the response. Thus, itis possible to reduce RTT and to stably realize the low delay livestreaming.

Furthermore, according to an aspect of the invention, there is provideda content distribution system including the content transmission deviceand the content playback device.

In the above configuration, the content distribution system has the sameeffects as those of the content transmission device and the contentplayback device.

Furthermore, a data structure of the content management information isincluded in the scope of the invention, which is associated with thecontent constituted by a plurality of segments that are acquired by thecontent playback device from the content transmission device and inwhich the segment is divided into the plurality of subsegments, andwhich includes acquisition source information indicating the acquisitionsource of the content where the byte range template is described.

Moreover, the content transmission device and the content playbackdevice may be realized by a computer. In this case, a control program inwhich the content transmission device and the content playback deviceare realized by the computer by causing the computer to function as eachmeans of the content transmission device and the content playbackdevice, and a computer readable recording medium in which the controlprogram is stored are also included in the scope of the invention.

The invention is not limited to the embodiments described above andvarious modifications are possible within the scope of the claims. Thatis, embodiments obtained by combining technical means that areappropriately modified in the scope of the claims are also includedwithin the technical scope of the invention.

[Realization Example by Software]

Finally, each block of the server 1 and the client 2, particularly, theserver control unit 11 and the client control unit 41 may be realized ashardware by a logic circuit formed on an integrated circuit (IC chip) ormay be realized as software using a Central Processing Unit (CPU).

In the latter case, the server 1 and the client 2 include the CPU thatexecutes a command of a program realizing each function, a Read OnlyMemory (ROM) in which the program is stored, a Random Access Memory(RAM) that develops the program, a storage device (recording medium)such as a memory in which the program and various data are stored, andthe like. Then, an object of the invention can also be achieved bysupplying the computer readable recording medium to the server 1 and theclient 2 on which a program code (executable program, intermediate codeprogram, and source program) of a control program of the server 1 andthe client 2 that are software realizing the above function is recordedand by reading and executing the program code that is recorded on therecording medium using the computer (or CPU or MPU).

As the recording medium described above, it is possible to use anon-transitory tangible medium, for example, tapes such as a magnetictape or a cassette tape, disks including a magnetic disk such as aFloppy (registered trademark) disk/hard disk or an optical disk such asCD-ROM/MO/MD/DVD/CD-R, cards such as an IC card (including memorycard)/optical card, semiconductor memories such as a maskROM/EPROM/EEPROM (registered trademark)/flash ROM, or logic circuitssuch as a Programmable logic device (PLD) or a Field Programmable GateArray (FPGA).

Furthermore, the server 1 and the client 2 may be configured to becapable of connecting to a communication network and the program codemay be supplied through the communication network. The communicationnetwork may transmit the program code and is not specifically limited.For example, it is possible to use the Internet, an intranet, anextranet, a LAN, an ISDN, a VAN, a CATV communication network, a VirtualPrivate Network, a telephone line network, a mobile communicationnetwork, a satellite communication network, and the like. Furthermore,the transfer medium configuring the communication network is also notlimited to a specific configuration or type as long as the transfermedium is a medium that is capable of transferring the program code. Forexample, the transmission of the program code also can be made in awired manner such as an IEEE1394, USB, a power line carrier, a cable TVline, a telephone line, and an Asymmetric Digital Subscriber Line(ADSL), and in radio such as infrared such as IrDA and remotecontroller, Bluetooth (registered trademark), IEEE802.11 wireless, aHigh Data Rate (HDR), a Near Field Communication (NFC), a Digital LivingNetwork Alliance (DLNA) (registered trademark), a mobile phone network,a satellite line, and a terrestrial digital network. Moreover, theinvention can be realized in a form of a computer data signal in acarrier wave in which the program code is also realized in electronictransfer.

INDUSTRIAL APPLICABILITY

The invention can be used in the content transmission device thattransmits the content of the MPEG-DASH standard and the content playbackdevice that acquires the content and performs the playback of thecontent.

REFERENCE SIGNS LIST

-   -   1 server    -   2 client    -   3 proxy    -   4 MPD storage device    -   5 segment storage device    -   6 content distribution system    -   21 content acquisition unit    -   22 content transmission unit (transmission means)    -   51 content acquisition unit (acquisition means)    -   52 content playback unit

1. (canceled)
 2. A content transmission device that transmits livedistribution content which is constituted by a plurality of segments inevery Representation for an AdaptationSet to a content playback device,the content transmission device comprising: management informationtransmission circuitry that transmits content management informationwhich is described in respect to (i) an offset indicated by a differencebetween a time when a segment is available and a time when at least aportion of the segment is available, and (ii) information indicatingwhether or not start times of subsegments of the segment are uniformbetween the Representations within the AdaptationSet to the contentplayback device.
 3. A content playback device that acquires livedistribution content which is constituted by a plurality of segments inevery Representation for an AdaptationSet and performs playback of thecontent, the content playback device comprising: management informationacquisition circuitry that acquires content management information whichis described in respect to (i) an offset indicated by a differencebetween a time when a segment is available and a time when at least aportion of the segment is available, and (ii) information indicatingwhether or not start times of subsegments of the segment are uniformbetween the Representations within the AdaptationSet.